Fence, timeline and android sync points

Daniel Vetter daniel at ffwll.ch
Thu Aug 14 08:58:48 PDT 2014

On Thu, Aug 14, 2014 at 10:12:06AM -0400, Jerome Glisse wrote:
> On Thu, Aug 14, 2014 at 09:16:02AM -0400, Rob Clark wrote:
> > On Wed, Aug 13, 2014 at 1:07 PM, Jerome Glisse <j.glisse at gmail.com> wrote:
> > > So this is fundamentaly different, fence as they are now allow random driver
> > > callback and this is bound to get ugly this is bound to lead to one driver
> > > doing something that seems innocuous but turn out to break heavoc when call
> > > from some other driver function.
> > 
> > 
> > tbh, that seems solvable by some strict rules about what you can do in
> > the callback.. ie. don't do anything you couldn't do in atomic, and
> > don't signal another fence.. off the top of my head that seems
> > sufficient.
> > 
> > If the driver getting the callback needs to do more, then it can
> > always schedule a worker..
> > 
> > But I could certainly see the case where the driver waiting on fence
> > sets everything up before installing the cb and then just needs to
> > write one or a couple regs from the cb.
> Yes sane code will do sane things, sadly i fear we can not enforce sane
> code everywhere especialy with out of tree driver and i would rather
> force there hand to only allow sane implementation. Providing call back
> api obviously allows them to do crazy stuff.

Well then don't support out of tree drivers. Fairly easy problem really,
and last time I checked "out of tree drivers suck" isn't a valid
objections for upstream code ... It's kinda assumed that they all do, it's
why we have staging after all.
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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